1. Field of the Invention
The present invention relates to drug delivery devices, and, in particular, to drug delivery devices that utilize an aerosol generator to nebulize a drug solution.
2. Description of the Related Art
Conventional ultrasonic drug nebulizing devices nebulize a drug solution by transmitting acoustic waves from an acoustic wave generator to the drug solution. Some of these devices transmit the acoustic waves from the acoustic wave generator to the drug solution through a fluid. Typically, these devices provide a barrier between the fluid and the drug solution. The barrier seals the drug solution from communication with the fluid, and also allows the acoustic waves from the aerosol generator to pass therethrough, from the transmitting fluid to the drug solution.
These barriers are typically composed of materials such as metal, which are generally considered suitable because their thermal and mechanical properties enable them to partially transmit the ultrasonic energy present in the acoustic waves from the fluid to the drug solution. However, known barrier materials like metallic materials still do not transmit all of the ultrasonic energy transmitted from the generator to the barrier, and therefore, form an energy sink within the device. This inhibits various aspects of the operation of typical nebulizing devices, such as, for example, nebulizing efficiency, flow rate, and the range of drug viscosities that can be nebulized.
Additionally, barrier materials are usually limited to materials that can be formed into a barrier and installed securely into nebulizing devices. Consequently, various materials that may provide enhanced barriers have not been used because there has not been a suitable mechanism for disposing a barrier composed of such materials within a nebulizing device.
In addition, for some materials the relative thickness and/or structural attributes of the barrier require careful balancing. The material should have sufficient structural integrity and strength to permit it to be securely sealed between the transmitting fluid and drug solution, yet at the same time sufficiently thin and flexible to transmit acoustic (ultrasonic) waves from the transmitting fluid to the drug solution. Heretofore, this balance has only been achieved with limited success.